A new class of fused ring .beta.-lactam antibiotics, including thienamycin and its semisynthetic derivatives, epithienamycins, and olivanic acids, has recently been described. These compounds which will be defined more extensively below, are hereinafter referred to as the "thienamycin class of compounds". These compounds have a high level of antibacterial activity, but are subject to extensive metabolism by mammalian species.
The kidney was identified as the primary site of metabolism, and an enzyme was purified from renal extracts which catalyzed the inactivation of thienamycin by hydrolysis of the .beta.-lactam. By such criteria as cytological localization, substrate specificity and susceptibility to enzyme inhibitors, this enzyme is very similar if not identical to a widely studied renal dipeptidase (E.C.3.4.13.11), also referred to in the literature as "dehydropeptidase peptidase I". However, the .beta.-lactamase activity is exhibited only toward the thienamycin class of compounds. Indeed, there exists no precedent example of the mammalian metabolism via .beta.-lactam cleavage of any representative of the classical .beta.-lactam antibiotics, the penicillins and cephalosporins.